In the first stage of this project we will study the effect of body temrperatures (core, mean skin, and ear temperatures) on ear blood flow in intact rabbits. Ear blood flow will be estimated through measurements of ear thermal conductance, obtained with heat flow discs. Internal temperature will be raised by an intravascular heat exchanger, and thermal conductance measured during central heating at different mean skin and ear temperatures. In similar experiments on intacts rabbits we will measure the effect of body temperatures on ear venous capacitance. Simultaneous measurements will be made of pressure and volume in ear veins during slow infusion of physiological solution into the veins in situ, with the ear isolated from the rest of the circulation by a pneumatic cuff. The studies on ear blood flow and venous capacitance will allow separation of the reflex and local factors which control cutaneous vascular function. In the second stage, we will study isolated rabbit ear arteries and veins to determine in vitro the influence of temperature on contractile responses. Isometric tension will be measured at temperatures from 7 degrees to 42 degrees C in response to exogenous nonepinephrine (NE). We will then investigate the mechanisms which are responsible for the change with temperature in contractile response. This will be done by determining the influence of temperature on smooth muscle contractility, release of NE during electrical field stimulation, uptake an degradation of NE, and the affinity of the Alpha-adrenoceptors on which NE acts. The combination of studies on intact animals and isolated vessels will elucidate the mechanisms underlying thermal control of cutaneous arteries and veins. An understanding of how temperature affects cutaneous vascular function will improve our ability to understand and treat disorders resulting from heat stress.